Conventional proppants are robust particles, such as sand, that are used to effectively “prop” open fractures created in geological formations during oil and gas drilling operations. Due to the fast settling time of sand in fracking fluids, viscosifying agents are used to suspend the sand to allow for effective pumping and improve the degree of proppant penetration into the fracked bed. These viscosifying agents require additional and/or stronger pumps, resulting in increased energy usage and/or higher capital cost, and consequentially, more operating cost. Additionally, the use of viscosifying agents has been found to produce poor (short) fractures in addition to damaging the fracture formation, resulting in decreased conductivity and decreased oil and gas output.
To alleviate issues surrounding the use of viscosifying agents, specialty ceramic and/or light weight proppants have been used. However, the highly engineered nature of these proppants greatly increases cost associated with the operation. Resin coated proppants (RCP) are an additional class of proppants where a polymer coating is used to trap pieces of broken proppant in the event of failure and additionally induce agglomeration of sand particles to prevent flowback.
Polymers used in RCP systems have been synthetic in nature and of the typical classes used for thermoset coatings: epoxies, polyesters, polyurethanes, etc. A recent technology utilized a hydrogel polymer coating of a superabsorbent material to suspend proppants during fracking operations. Superabsorbent materials used in these hydrogel-coated RCPs utilize anionic or neutral charge moieties. However, the performance of these superabsorbents progressively diminishes as the dissolved ion concentration increases. This effect is more pronounced when multivalent ions (e.g., divalent cations) are present such as in hard water conditions, likely due to a cross linking effect of the multivalent cation on the negatively charged sodium polyacrylate superabsorbent and resulting in inhibited swelling capacity. High ionic concentrations and hardness are typical characteristics of water available in fracking locations and as a result, these materials are limited to very specific usage scenarios where relatively pure water is required (tap water or water containing low total dissolved solids (TDS)). Additionally, even in scenarios where water is pure, it is likely that conditions within the well can harden otherwise more pure water and further decrease performance.